1. Field of the Invention
The present invention relates to centrifugal pumps, and more particularly, to an improved pumping system for a multi-stage centrifugal pump. The present invention finds particular application in conjunction with an aircraft fuel pump, and it will be described with particular reference thereto. However, it will be appreciated that the present invention is also amenable to other like applications.
2. Discussion of the Art
Centrifugal pumps generally include at least one impeller which rotates within a casing or housing. A motor rotates the impeller via a shaft which operatively connects the motor to the impeller. Fluid is provided to the impeller through, for example, a centrally disposed inlet located on one or both faces of the impeller. Fluid enters the impeller inlet in an axial direction and, due to the rotation of the impeller, flows radially outwardly. Finally, the fluid discharges from the impeller along a peripheral edge of the impeller. Meanwhile, the fluid flowing outwardly from the impeller creates a suction at the central inlet of the impeller which serves to continuously draw more fluid into the inlet.
The fluid discharged from the impeller exits at a significantly higher pressure than the fluid entering the impeller. The major portion of the energy imparted to the fluid is converted to a pressure head by means of a volute, diffuser, or other system. When high fluid pressures are desired, multi-stage centrifugal pumps are often employed. In a multi-stage pump, the fluid through the pump proceeds through successive centrifugal processes or stages. In each stage, the fluid enters an impeller and is centrifugally forced radially outwardly as described above. Each stage incrementally imparts rotational energy into the fluid thereby successively increasing the pressure of the fluid.
Aircraft engines are an application where high fuel pressures are required. However, the fuel is often required to be delivered at a high pressure for only a short period of time. During the majority of the operation of the pump, fuel is only required to be delivered at a low pressure. Heretofore, multi-stage pumps were used for the delivery of fuel during both of these peak and off-peak periods with little or no means to selectively deactivate the stages of the pump. As a result, large losses in pump efficiency occurred.
Thus, it is desirable to provide a multi-stage pump whereby each stage may be selectively actuated and deactuated. Such a pump would allow all stages of a multi-stage pump to be activated when high pressure is required and less stages when low pressure will suffice. The present invention contemplates such an invention.
In accordance with the present invention, an improved multi-stage centrifugal pumping system is provided for minimizing the above-referenced and other disadvantages of the prior art, and in particular, for minimizing losses due to the use of multi-stage centrifugal pumps in applications where the fluid pressure requirements fluctuate over relatively short periods of time.
In accordance with one aspect of the present invention, a pumping system for selectively activating the stages of a multi-stage centrifugal pump is provided. The pumping system has a first stage impeller for receiving fluid into the system and imparting rotational energy into the fluid. The system also has a second stage impeller for imparting additional rotational energy into the fluid after the first stage impeller. The system includes a valve for selectively opening and closing an inlet to the second stage impeller.
The valve includes a first inlet in fluid communication with the first stage impeller, a first outlet in fluid communication with the inlet of the second stage impeller, a second inlet in fluid communication with an outlet from the second stage impeller, and a second outlet allowing fluid to exit the pumping system. The valve is selectively actuated between first and second positions. In the first position of the valve fluid exiting the first stage impeller enters the second stage impeller. The second position of the valve prevents fluid from entering the second stage impeller.
In the second position the valve allows fluid to flow toward the outlet of the second stage impeller and to exit the valve through the second outlet. Additionally, in the second position the valve causes fluid to flow toward the outlet of the second stage impeller and prevents fluid from flowing toward the inlet of the second stage impeller which causes the impeller to become free wheeling and have a zero flow rate.
One advantage of the present invention is that it eliminates or substantially reduces losses due to fluctuating fluid pressure requirements.
Further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiment.